1. Field of the Invention
The present invention relates to a high-frequency circuit board used for transmission/reception in a high-frequency band, particularly the millimeter-wave band, and also to a semiconductor device using the high-frequency circuit board.
2. Background Art
One known switch for switching signals is employed in 15 transmission equipment, reception equipment, and transmission/reception modules used for radar or for communications in the microwave or millimeter-wave band.
FIG. 15 is a plan view of a conventional switch MMIC (Monolithic Microwave IC) chip, and FIG. 16 is a circuit diagram showing an equivalent circuit of the switch.
Referring to FIG. 15, reference numeral 100 denotes a switch MMIC chip; 102 a GaAs substrate; 104 an FET; 104a a source electrode; 104b a drain electrode; 104c a gate electrode; 104d an air-bridge wire interconnecting source electrodes 104a; 106 an input terminal; 108 an input line; 110 an air-bridge wire bridging between the input line 108 and each drain electrode 104b; 112 an output line; 114 a connection line connecting between the output line 112 and each drain electrode 104b; 116 an output terminal; and 118 a via hole connected to each source electrode 104a and to a grounding conductor disposed on the back surface of the GaAs substrate 102.
Furthermore, in the figure, reference numeral 120 denotes a gate signal input terminal, and 122 denotes a control signal line connected to each gate electrode 104c. Reference numeral 124 indicates a capacitor having a first end connected to the control signal line 122 and a second end connected to a via hole 126, which is further connected to the grounding conductor disposed on the back surface of the GaAs substrate 102. Reference numeral 128 denotes a resistor.
In FIG. 16, the input line 108 and the output line 112 each have a characteristic impedance of 50 xcexa9. The switch 100 supplies an ON/OFF signal from the gate signal input terminal to each gate electrode 104c to pass or cut off a high-frequency signal applied to the input terminal 106. When the high-frequency signal is passed from the input terminal 106 to the output terminal 116, the FET 104 is in the OFF-state, and therefore can be regarded as a capacitor having the off-capacitance of the FET. This means that the high-frequency signal is output to the output terminal 116 through a filter composed of the inductance components of the input line 108 and the output line 112 and the off-capacitance of the FET 104.
In the conventional switch 100 having a configuration as described above, the FET 104 formed on the GaAs substrate 102 is composed of a plurality of FET devices. Accordingly, the value of the off-capacitance of the FET 104 may vary when not all of the FET devices have identical electrical characteristics, which occurs depending on position of the wafer on which the switch 100 is formed or which is caused by process variations.
Especially, when the conventional switch MMIC was applied to a millimeter-wave band, a variation in the off-capacitance affected the filter characteristics and, as a result, the frequency characteristics of the switch varied, reducing the yield of the switch in some cases.
In order to solve the above problems, it is a first object of the present invention to provide an inexpensive high-frequency circuit board used for switches having good high-frequency characteristics. A second object of the present invention is to provide an inexpensive and highly reliable semiconductor device using such a high-frequency circuit board.
According to one aspect of the present invention, a high-frequency circuit board comprises a dielectric substrate, and a high-frequency signal line is mounted on a main surface of said dielectric substrate and has an input end and an output end for high-frequency signals. Another signal line is disposed on said main surface along said high-frequency signal line, and a first grounding conductor is disposed on said main surface along said high-frequency signal line.
In another aspect, in the high-frequency circuit, said high-frequency signal line may have a plurality of branch portions along which said first grounding conductor and said another signal line are disposed.
In another aspect, the high-frequency circuit may further comprise a second grounding conductor. The first grounding conductor is disposed on one side of said high-frequency signal line with said another signal line between said first grounding conductor and said high-frequency signal line, and said second grounding conductor is preferably disposed along said high-frequency signal line on the other side of said high-frequency signal line.
According to another aspect of the present invention, a semiconductor device comprises a high-frequency circuit board as described above and a plurality of bumps disposed on said high-frequency signal line, said another signal line, and said first grounding conductor of said high-frequency circuit board. Further, a semiconductor chip is disposed on said high-frequency circuit board. The semiconductor chip includes a semiconductor substrate and a transistor disposed on said semiconductor substrate, and the transistor has a control electrode, a first electrode, and a second electrode, wherein said control electrode is connected to said another signal line through one of said plurality of bumps, said first electrode is connected to said first grounding conductor through one of said plurality of bumps, and said second electrode is connected to said high-frequency signal line through one of said plurality of bumps.